1. Field of the Invention
The present invention relates to a flame retarding polyester composition superior in thermal stability, fluidity and mechanical properties.
2. Description of the Prior Art
Thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexane dimethylene terephthalate, etc. have found applications in mechanical components, electrical parts, motor vehicle parts and the like. On the other hand, for industrial materials as described above, safety against flames, i.e. flame retardancy, has been strongly required. Besides balancing general chemical and physical properties, with the further requirement that, during injection molding of molded items or heat treatment thereof, the flame retarding agent does not bleed out onto the surfaces of the molded items.
Conventionally, as non-bleed type flame retarding agents for the thermoplastic polyester, there have been proposed polymeric flame retarding agents such as a halogenated polycarbonate (Japanese Laid Open Patent Application Tokkaisho No. 48-52834) and a halogenated epoxy resin (Japanese Patent Publication Tokkosho No. 53-18068), etc. Although the known flame retarding agents as described above, which are mainly composed of tetrabromobisphenol A, are superior in compatibility with respect to polyester, they tend to deteriorate the crystallinity inherent in polyester, thus adversely affecting the mechanical properties, thermal stability, chemical resistance, and electrical properties, etc. of the polyester itself.
Meanwhiile, there have also been introduced halogen containing polystyrene and halogen containing poly-.alpha.-methylstyrene, together with their applications to thermoplastic polyesters (Plastic Technology, July, 1980, pages 71-74), but in the polyester compounds in which the above flame retarding agents are mixed, marked deterioration of thermal stability and mechanical properties is noticed, with simultaneous reduction of fluidity, thus resulting in poor moldability.
Therefore, it is desirable to develop polyester compounds which exhibit superior flame retarding and favorable mechanical properties and which also are free of disadvantageous bleeding of the flame retarding agent.